FIG. 1 is a schematic view of a single crystal silicon pulling device.
A single crystal silicon pulling device 10 is provided, in a furnace 1 thereof, with a heat insulator 2 that is provided inside an inner wall of the furnace 1 and insulates heat transfer from the inside/outside of the furnace 1; a crucible 3 that maintains a silicon material such as polycrystalline silicon and in which the silicon melt obtained after the silicon raw material is melted is reserved; a heater 4 that is arranged so as to surround the crucible 3 and heats the silicon material by way of the crucible 3; and a thermal shielding body 5 that is arranged above the crucible 3 so as to surround a pulling path of a single crystal silicon 8.
Additionally, a cooling coil 6 may be provided above the crucible 3 so as to surround the pulling path of the single crystal silicon 8. The cooling coil 6 is formed such that a pipe in which cooling water flows is coiled in a helical shape, and has a cylindrical shape as a whole. The cooling coil 6 is arranged above the crucible 3 such that the pulling path of the crystal is positioned inside the coil. By increasing the cooling rate of the single crystal silicon 8 through the cooling coil 6, quality of the crystal can be improved due to the fact that the size of the hole type defect included in the single crystal silicon 8, namely, COP becomes small. Additionally, the production cycle can be accelerated, thereby improving the production efficiency. It should be noted that, in a case of controlling oxygen precipitation or of improving the oxide film pressure resistance characteristic, a cylindrical-shaped heater or a purge tube may be provided in place of the cooling coil 6 to approximately the same location as the cooling coil.
Here, a procedure of a manufacturing process of the single crystal silicon using the single crystal silicon pulling device 10 will be briefly described. The silicon material is put into the crucible 3 and the heater 4 is activated. The silicon material is heated and melted, and then the silicon melt is generated. A seed crystal of silicon is immersed into the generated silicon melt. By pulling up the immersed seed crystal, the single crystal silicon 8 is grown around the seed crystal. During pulling up the single crystal silicon 8, a pulling up speed, location of the thermal shielding body 5, and the like are adjusted. Furthermore, by making the cooling water flow in the pipe of the cooling coil 6, the single crystal silicon 8 is forcefully cooled.
Ar gas is supplied from above in the furnace 1 during the growth of the single crystal silicon 8. FIGS. 5A and 5B are diagrams showing gas flows in a general furnace. FIG. 5A shows a gas flow during the early stages of growth of the single crystal silicon. FIG. 5B shows a gas flow after the early stages of growth of the single crystal silicon.
As shown in FIG. 5A, during the early stages of growth of the single crystal silicon, the Ar gas supplied from above in the furnace 5 passes through the inside of the cooling coil 6 and falls down to the vicinity of the silicon melt. Furthermore, the Ar gas passes down between the crucible 3 and the heater 4, and drains from a gas outlet 1a provided in the lower part of the furnace 1 to the outside of the furnace 1. Additionally, after passing through the inside of the cooling coil 6, part of the Ar gas supplied from above in the furnace 5 passes through between a lower end 6a of the cooling coil 6 and the thermal shielding body 5, moves upward through between the cooling coil 6 and the thermal shielding body 5, and then merges with Ar gas supplied from above in the furnace 5.
As shown in FIG. 5B, after the early stages of growth of the single crystal silicon, part of the Ar gas supplied from above in the furnace 5 passes through the inside of the cooling coil 6, in other words, a space between the cooling coil 6 and the single crystal silicon 8 and falls down to the vicinity of the silicon melt. Furthermore, the Ar gas passes down between the crucible 3 and the heater 4, and drains from a gas outlet 1a provided in the lower part of the furnace 1 to the outside of the furnace 1. Additionally, part of the Ar gas supplied from above in the furnace 5 falls down between the cooling coil 6 and the thermal shielding body 5, passes through between the lower end 6a of the cooling coil 6 and the thermal shielding body 5, and then merges with the Ar gas passing through the inside of the cooling coil 6.